1. Field of the Invention
The present invention relates to a method for producing a frozen product of deep-fat (oil-cooked) fried food (frozen fried food) for a microwave oven cooking, particularly a microwave cooking-oriented frozen food of a deep-fat (oil-cooked) fried food, such as croquettes, breaded fried shrimps, squid fritters, chicken cutlets, beef cutlets, and the like, as well as a frozen fried food thus obtained or which can be obtained in the method.
A frozen product of cooked fried food such as a deep-fat fried croquette and a breaded fried shrimp can be stored for a prolonged period and can readily be consumed after thawing and re-heating it. A trend of a recent increase in the number of working women or of people who are active late at night or early in the morning causes a change in a lifestyle, a marked spread of the use of a microwave oven, and an increase in the number of convenience stores, food courts or roadside restaurants, which lead to an increased demand of frozen foods which can readily be served after microwave cooking. There are a large number of the types of core materials (filling materials; xe2x80x9cGuzaixe2x80x9d in Japanese) especially of fried foods, and the lighter crispness (crunchiness; good eating quality) peculiar to the breading (coat; xe2x80x9cKoromoxe2x80x9d in Japanese) of any of such foods in harmony with juicy core materials is preferred widely.
2. Description of the Related Art
A frozen fried food has conventionally been produced by freezing the food directly after a thorough oil cooking similarly to an ordinary fried food. In the case of a fried food whose crispness (crunchiness) is favored, a conventional method for freezing, however, poses a problematic loss of the crispness associated naturally with a fried food, since the breading of the fried food is softened and moistened by the water generated from the core materials upon the microwave cooking just before eating. This softening of the breading due to the migration of water tends to be marked much more problematically after being stored frozen for a prolonged period longer.
In order to solve the problems described above, various technologies have been proposed. Those which can be exemplified are a method for keeping the surface of a breading at a low water content by retarding the migration of the water generated from the core materials to the breading surface layer which is achieved by an oil cooking followed immediately by a quick freezing followed by a storage as being frozen at a temperature of xe2x88x9230xc2x0 C. or lower (refer to JP-A-6-141788), a method for drying a breading by blowing a dried air at 0 to 15xc2x0 C. before freezing (refer to JP-A-51-7137), a method for preventing an ooze-out of water upon a microwave cooking by dehydrating a pre-processed core materials, by a microwave heating under reduced pressure and the like (refer to JP-A-11-266801), a method for maintaining a crispness by freezing a deep-fat fried food together with a desiccant as being wrapped with a water vapor-impermeable film whereby drying a breading during the freezing (refer to JP-A-5-64574), a method for preventing the softening of a breading due to the migration of water from the core materials by forming a double-layered structure comprising a first breading formed by steaming a purified starch and a second breading formed on the surface of said first breading by oil-cooking a deep-frying batter consisting mainly of a wheat flour for flying (refer to JP-A-11-123055), a method for improving the crispness of a breading material itself by producing a frozen fried food from a dry breading (crumb) mixed with a corn flour (refer to JP-A-4-53459), a method for improving the crispness by coating a fried food with an edible aqueous solution of pullulan, wafer, gelatin and the like (refer to JP-A-2-283248), and the like.
On the other hand, the following methods are known for freezing a food for producing a frozen food (see, xe2x80x9cSHOKUHIN KIKAI SOUCHI (Machinery and equipment for food industry)xe2x80x9d, p64-68 (1995), xe2x80x9cREITOU (Refrigeration)xe2x80x9d, Vol. 70, No. 809 (1995), xe2x80x9cREITOU (Refrigeration)xe2x80x9d, Vol. 61, No. 703, and the like).
(a) Gas contact freezing method (air blast freezing method)
It is used most frequently, and comprises blowing an air at about (approximately) xe2x88x9235 to xe2x88x9240xc2x0 C. at a flow rate of about 5 to 10 m/sec to effect freezing.
(b) Solid contact freezing method (contact freezing method)
It comprises bringing a subject food into a direct contact with a metal plate cooled at about xe2x88x9235 to xe2x88x9240xc2x0 C. to effect freezing.
(c) Liquefied gas spray freezing method
It comprises a direct spraying of a low temperature liquefied gas such as a liquid carbon dioxide (CO2), a liquid nitrogen (N2), and the like onto a subject food and utilizing a latent heat of evaporation and a sensible heat to effect freezing.
(d) Liquid immersion freezing method
It comprises a direct immersion of a subject food in a low temperature liquid (for example, calcium chloride brine, ethanol brine, propylene glycol brine, liquid carbon dioxide, liquid nitrogen, and the like) to effect freezing.
Any of these conventional freezing methods can generally be referred to as xe2x80x9ca quick freezing methodxe2x80x9d. A quick freezing is defined as a process in which the time period required for the food temperature to be lowered across the maximum ice crystal forming range of xe2x88x921 to xe2x88x925xc2x0 C. is not longer than 30 minutes or a moving speed of the freezing front V as a distance over which the freezing boundary front is advanced per one hour from the surface to the internal region of a food is 5 to 20 cm/h. Nevertheless, such condition of a quick freezing is not satisfied precisely in most of the cases, and used mostly rather as a guideline for ensuring a normal freezing operation in a manufacturing process (refer to NIPPON SHOKUHIN KOGYO GAKKAISHI (Journal of the Japanese society for food science and technology), 39, 7, 608 (1992)).
Processes (a) to (d) each of which is referred to xe2x80x9ca quick freezing methodxe2x80x9d use practically diverse cooling rates and freezing efficiencies, and are selected appropriately based on the condition and the quality of a food product to be frozen being weighed against a cost. Especially in Process (d), a very low temperature such as xe2x88x92196xc2x0 C. under atmospheric pressure (with a liquid nitrogen) and xe2x88x9220xc2x0 C./1.96 MPa (liquid carbon dioxide) is utilized without any need of consideration for the effect of the heat transfer, i.e., the effect of the heat transmitted from air to a food product, whereby enabling a very quick freezing when compared with a gas contact method used mainly these days. Accordingly, a quality which can not be expected by any of Processes (a) to (c) is associated characteristically.
A freezing method of Process (d) described above is used usually in processing a raw material (perishable foodstuff) before cooking consisting of cells such as a tuna fish and a livestock meat especially in which an improved quality is beneficial significantly, since it uses a very quick freezing which allows an intracellular water to become a fine ice crystal, thus enabling a freezing without any damage on a food matrix resulted from the growth of the ice crystal. However, this ability of preventing a cell destruction itself can not be expected to contribute to an achievement of an increased crispness (crunchiness; better eating quality) of a cooked frozen fried food, and no positive application of such very quick freezing method to a production of a frozen product of deep-fat (oil-cooked) fried food for a microwave oven cooking can be found.
Problems to be Solved by the Invention
Among the conventional methods described above, the method using a direct drying of the core materials (filling materials) and the breading material allows the water associated originally with the core materials to be lost significantly, resulting in a significant reduction in the juiciness of the core materials which is desirable in a fried food, while the method for improving the characteristics of a breading material also suffering from an insufficiency in eliminating the problematic migration of the water into the breading layer during a storage as being frozen.
Thus, the present invention is intended to solve the problems described above, and its objective is typically to provide a method for producing a frozen product of deep-fat fried food (frozen fried food) capable of exhibiting, after a microwave oven heating, a favorable crispness of a breading like one experienced just after frying while preserving a juiciness associated originally with core materials and also capable of maintaining the original juiciness and crispness feeling even after a prolonged storage in a domestic freezer.
Disclosure of the Invention
A method for producing a frozen fried food for a microwave cooking, particularly a frozen product of deep-fat (oil-cooked) fried food for a microwave cooking according to the present invention with which the objective described above can be accomplished is based on a method comprising the step of a freezing of, particularly a very quick freezing (an immediate quick freezing) of a deep-fat fried food, preferably immediately after oil-cooking thereof, at a moving speed of the freezing front of 20 cm/h or higher, preferably of exceeding 20 cm/h, more preferably of 40 cm/h or higher, and also encompasses the following aspects in the present invention.
(1) A method for producing a frozen fried food for a microwave oven cooking, comprising the step of a freezing of, preferably a very quick freezing (an immediate quick (rapid) freezing) of, a deep-fat (an oil-cooked) fried food, more preferably immediately after oil-cooking thereof, at a moving speed of the freezing front exceeding 20 cm/h.
(2) A method for producing a frozen fried food for a microwave oven cooking, comprising the step of freezing a deep-fat fried food, preferably immediately after oil-cooking thereof, at a moving speed of the freezing front exceeding 20 cm/h followed by a storage of the frozen food thus obtained at a temperature of xe2x88x9210xc2x0 C. or lower.
(3) A method for producing a frozen fried food for a microwave oven cooking according to the above Section (1) or (2), wherein said moving speed of the freezing front is 40 cm/h or higher.
(4) The method according to any one of the above sections (1) to (3), wherein said freezing is conducted by a method selected from a liquid nitrogen immersion method and a liquid carbon dioxide immersion method.
(5) The method according to any one of the above sections (2) to (4), wherein said temperature at which said frozen food is stored is within the range from xe2x88x9210xc2x0 C. to xe2x88x9225xc2x0 C.
(6) A frozen fried food for a microwave cooking, which is or can be obtained in the method according to any one of the above sections (1) to (5).